Internal combustion engines convert chemical energy from a fuel into mechanical energy. The fuel may be petroleum-based, natural gas, another combustible material, or a combination thereof. Most internal combustion engines inject an air-fuel mixture into one or more cylinders. The fuel ignites to generate rapidly expanding gases that actuate a piston in the cylinder. The fuel may be ignited by compression such as in a diesel engine or through some type of spark such as the spark plug in a gasoline engine. The piston usually is connected to a crankshaft or similar device for converting the reciprocating motion of the piston into rotational motion. The rotational motion from the crankshaft may be used to propel a vehicle, operate a pump or an electrical generator, or perform other work. A vehicle may be a truck, an automobile, a boat, or the like.
Many internal combustion engines have a turbocharger to pressurize or boost the amount of air flowing into the cylinders. The additional air in a cylinder permits the combustion of additional fuel in the cylinder. The combustion of additional fuel increases the power generated by the engine. Generally, an internal combustion engine produces more power with a turbocharger than without a turbocharger.
Most turbochargers have a turbine connected to a compressor. The turbine usually has a turbine wheel positioned to spin inside a turbine housing. The compressor usually has a compressor wheel positioned to spin inside a compressor housing. The turbine wheel usually is connected to the compressor wheel via a common shaft. The turbocharger typically is mounted near the exhaust manifold of the engine. The exhaust gases from the engine pass through the turbine housing. The exhaust gases cause the turbine wheel to spin, thus causing the compressor wheel to spin. The spinning compressor wheel pressurizes the intake air flowing through the compressor housing to the cylinders in the engine.
Turbochargers typically operate in response to the engine operation. Generally, a turbocharger spins faster when the engine produces more exhaust gases and spins slower when the engine produces less exhaust gases. If the turbocharger operates too fast, the turbocharger output may reduce engine performance and may damage the turbocharger and other engine components. If the turbocharger operates too slow, the engine may hesitate, loose power, or otherwise operate inefficiently. The turbocharger efficiency also may be affected by changes in atmospheric pressure, ambient temperature, and engine speed.
Turbochargers may have various configurations to control the output from the turbocharger. Many turbocharger configurations may have a wastegate or a valve to allow exhaust gases to bypass the turbine. Other turbocharger configurations may use a turbine with a variable geometry, where a vane or nozzle inside the turbine housing moves to increase or decrease the exhaust gas flow across the turbine wheel. Some turbocharger configurations may have two compressors connected via a common shaft to the turbine. Yet other turbocharger configurations may have two turbochargers.
Dual turbochargers usually have a first turbocharger and a second turbocharger that are connected to receive exhaust gases and to pressurize the intake air flowing to the cylinders. The first turbocharger usually operates during a one range of intake air pressures. The second turbocharger usually operates during another range of air intake pressures. The first turbocharger may operate during lower intake air pressures. The second turbocharger may operate at higher intake air pressures. The first turbocharger may operate at substantially all intake air pressures, while the second turbocharger may operate at higher intake air pressures. The first and second turbochargers may operate at the same or different times, and may operate together during a transition time when the second turbocharger is activated.
Many turbochargers are mounted on an internal combustion engine by bolts or similar mounting mechanism. The bolts typically pass through holes in a turbocharger base or flange and screw into holes in the internal combustion engine. The connection between the turbocharger base and the internal combustion engine may be mismatched such as when the turbocharger base and engine are uneven, when the holes on the turbocharger base do not align with the holes in the engine, and the like. The turbocharger may be mounted on the engine when the turbocharger base and engine are mismatched. The mismatched connection may create mechanical or installed stresses in the turbocharger and mounting mechanism.
In addition, the hot exhaust gases may cause thermal stresses during operation of the turbocharger. The exhaust gases may raise the temperature of the turbocharger up to about 1500° F. (815° C.) or more. The temperature increase causes thermal expansion of the turbocharger. The temperature decreases when the turbocharger stops operating. The temperature decrease causes thermal contraction of the turbocharger. The thermal expansion and contraction creates thermal stresses within the turbocharger.
These installed and thermal stresses may cause cracking, fatigue, fracture, or other failure of the turbocharger structure. The installed and thermal stresses may increase shear forces or side loads on the mounting bolts or mounting mechanism. The thermal and installed stresses may be more pronounced in dual turbochargers, larger turbochargers such as turbochargers used in diesel engines, and in other turbochargers with a larger or longer connection area with the engine. The size and type of connection area may increase the effect of thermal stresses and may increase the potential for mismatch of the turbocharger with the engine.
Some dual turbochargers have a single-mounting mechanism, where a supporting turbocharger is mounted on the internal combustion engine. The other turbocharger is mounted directly to the supporting turbocharger and not on the internal combustion engine. The supporting and other turbochargers may be difficult or awkward to install as a unit and may increase the engine assembly time if installed separately. The uneven support of a single-mounting mechanism may increase the maintenance of the turbocharger. In addition, the geometry of a single-mounted dual-turbocharger assembly may not be rigid enough to adequately support both turbochargers against engine and turbocharger vibration energy. The noise vibration and harshness may be transmitted to the vehicle and operator.